Solid-state imaging device and manufacturing method therefor

ABSTRACT

A solid-state imaging device includes a first and second pixel regions. In the first pixel region, a photoelectric conversion unit, a floating diffusion region (FD), and a transferring transistor are provided. In the second pixel region, an amplifying transistor, and a resetting transistor are provided. A first element isolation portion is provided in the first pixel region, while a second element isolation portion is provided in the second pixel region. An amount of protrusion of an insulating film into a semiconductor substrate in the first element isolation portion is smaller, than that in the second element isolation portion.

TECHNICAL FIELD

The present invention relates to a solid-state imaging device.

BACKGROUND ART

A configuration of a solid-state imaging device is known, in which aphotoelectric conversion unit and a peripheral circuit unit areallocated to and formed on separate substrates, respectively, andconnected electrically to each other by microbumps or the like.

Japanese Patent Application Laid-Open No. 2009-170448 discusses aback-side surface irradiation type solid-state imaging device configuredsuch that a first semiconductor on which pixels each including aphotoelectric conversion unit and a reading circuit for reading signalstherefrom are arranged, is bonded to a second semiconductor on which asignal processing for processing signals read from the pixels isarranged. The reading circuit includes transistors such as atransferring transistor, an amplifying transistor, and a resettingtransistor.

In the solid-state imaging device discussed in Japanese PatentApplication Laid-Open No. 2009-170448, at least the resetting transistoris arranged on the first semiconductor substrate on which thephotoelectric conversion unit is arranged. An element isolationstructure according to element isolation due to insulating film arrangedin the semiconductor substrate, such as local oxidation of silicon(LOCOS) isolation, or shallow trench isolation (STI), is necessary forelement isolation of the resetting transistor or the amplifyingtransistor from the photoelectric conversion unit. Dark current isliable to be generated at an interface between the insulating filmarranged in a semiconductor substrate and the semiconductor substrate.Accordingly, when the element isolation structure due to the insulatingfilm arranged in the semiconductor substrate is used for elementisolation of the photoelectric conversion unit, dark current easilyflows into the photoelectric conversion unit. The dark current flowinginto the photoelectric conversion unit causes noise. Noise generated ata preceding stage at which signals are amplified by the amplifyingtransistor dominantly affects image quality, as compared with noisegenerated at a subsequent stage of the amplifying transistor.

When the insulating film arranged in the semiconductor substrate is notused for element isolation of the resetting transistor and thephotoelectric conversion unit, a wider element isolation region isneeded to electrically isolate the resetting transistor and thephotoelectric conversion unit from each other. Thus, if the lightreceiving area of the photoelectric conversion unit is set to beconstant in order to maintain sensitivity of the photoelectricconversion unit, a pitch of the pixels increases. Consequently, it isdifficult to miniaturize the pixels.

CITATION LIST Patent Literature

-   PTL 1: Japanese Patent Application Laid-Open No. 2009-170448

SUMMARY OF INVENTION

The present invention aims at providing a solid-state imaging devicefavorable to reducing noise caused by dark current generated in anelement isolation region for isolating a resetting transistor or anamplifying transistor from a photoelectric conversion unit, and tominiaturizing pixels.

According to an aspect of the present invention, a solid-state imagingdevice having a plurality of pixels each of which includes aphotoelectric conversion unit, a floating diffusion region, atransferring transistor including a transferring gate electrodeconfigured to transfer signal charge generated at the photoelectricconversion unit to the floating diffusion region, an amplifyingtransistor configured to output a signal based on an amount of electriccharge of the floating diffusion region, and a resetting transistorconfigured to reset a voltage of the floating diffusion region. Thesolid-state imaging device further includes a first semiconductorsubstrate and a second semiconductor substrate. In the solid-stateimaging device, a first insulating film is provided on a first principalsurface of the first semiconductor substrate. The first semiconductorsubstrate includes a first pixel region. A plurality of photoelectricconversion units and a plurality of floating diffusion regions arearranged like a matrix on the first pixel region. A first elementisolation portion for electrically isolating the plurality ofphotoelectric conversion units from the plurality of floating diffusionregions is arranged in the first pixel region. A second insulating filmis arranged on the second semiconductor substrate. The secondsemiconductor substrate includes a second pixel region. A plurality ofthe amplifying transistors and a plurality of the resetting transistorsare arranged on the second pixel region like a matrix. A second elementisolation portion for electrically isolating the plurality of theamplifying transistors from the plurality of the resetting transistorsis arranged in the second pixel region. An interface between the firstsemiconductor substrate and the first insulating film in the firstelement isolation portion is arranged at a first depth with respect toan interface between the first semiconductor substrate and the firstinsulating film in the photoelectric conversion unit. An interfacebetween the second semiconductor substrate and the second insulatingfilm in the second element isolation portion is arranged at a seconddepth with respect to an interface between the second semiconductorsubstrate and the second insulating film in a region in which theamplifying transistor is provided. The first depth is shallower than thesecond depth.

The solid-state imaging device according to the present invention canreduce noise caused by dark current generated in an element isolationregion for isolating a resetting transistor or an amplifying transistorfrom a photoelectric conversion unit, and miniaturize pixels.

Further features and aspects of the present invention will becomeapparent from the following detailed description of exemplaryembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate exemplary embodiments, features,and aspects of the invention and, together with the description, serveto explain the principles of the invention.

FIG. 1A is a schematic diagram illustrating planar configurations ofsubstrates.

FIG. 1B is a schematic diagram illustrating planar configurations ofsubstrates.

FIG. 1C is a schematic diagram illustrating planar configurations ofsubstrates.

FIG. 2 is a circuit diagram illustrating an equivalent circuit of apixel unit of a first exemplary embodiment of a solid-state imagingapparatus according to the present invention.

FIG. 3 is an equivalent circuit diagram illustrating an equivalentcircuit of a signal processing circuit of the first exemplary embodimentof the solid-state imaging apparatus according to the present invention.

FIG. 4 is a schematic diagram illustrating a cross-sectional structureof the first exemplary embodiment of the solid-state imaging deviceaccording to the present invention.

FIG. 5A is a schematic diagram illustrating a planar structure of thepixel unit of the first exemplary embodiment of the solid-state imagingdevice according to the present invention.

FIG. 5B is a schematic diagram illustrating a planar structure of thepixel unit of the first exemplary embodiment of the solid-state imagingdevice according to the present invention.

FIG. 6 is an equivalent circuit diagram illustrating a pixel unit of asecond exemplary embodiment of a solid-state imaging device according tothe present invention.

FIG. 7 is a schematic diagram illustrating a planar structure of thepixel unit of the second exemplary embodiment of the solid-state imagingdevice according to the present invention.

FIG. 8 is a schematic diagram illustrating a planar structure of a pixelunit of a modification of the second exemplary embodiment of thesolid-state imaging device according to the present invention.

FIG. 9 is a schematic diagram illustrating a cross-sectional structureof a third exemplary embodiment of a solid-state imaging deviceaccording to the present invention.

FIG. 10 is an equivalent circuit diagram illustrating an equivalentcircuit of each of a pixel unit and a signal processing circuit of afourth exemplary embodiment of a solid-state imaging device according tothe present invention.

FIG. 11 is a schematic diagram illustrating a cross-sectional structureof the fourth exemplary embodiment of the solid-state imaging deviceaccording to the present invention.

FIG. 12A is a schematic diagram illustrating a cross-sectional structureof a modification of the first exemplary embodiment of the solid-stateimaging device according to the present invention.

FIG. 12B is a schematic diagram illustrating a cross-sectional structureof a modification of the first exemplary embodiment of the solid-stateimaging device according to the present invention.

FIG. 12C is a schematic diagram illustrating a cross-sectional structureof a modification of the first exemplary embodiment of the solid-stateimaging device according to the present invention.

FIG. 13A is a cross-sectional diagram illustrating a manufacturingmethod according to the first exemplary embodiment of the solid-stateimaging device according to the present invention.

FIG. 13B is a cross-sectional diagram illustrating a manufacturingmethod according to the first exemplary embodiment of the solid-stateimaging device according to the present invention.

FIG. 13C is a cross-sectional diagram illustrating a manufacturingmethod according to the first exemplary embodiment of the solid-stateimaging device according to the present invention.

DESCRIPTION OF EMBODIMENTS

Various exemplary embodiments, features, and aspects of the inventionwill be described in detail below with reference to the drawings.

Hereinafter, a configuration of treating an electron as a signal chargeis described by way of example. However, the present invention can beapplied to a configuration treating a hole as a signal charge, bychanging a conductivity type of a semiconductor region to an oppositeconductivity type.

A first exemplary embodiment of a solid-state imaging device to whichthe present invention is applied is described hereinafter. FIG. 1A is aschematic diagram illustrating a planar configuration of each of a firstand second semiconductor substrates included in a solid-state imagingdevice according the present exemplary embodiment. According to thepresent exemplary embodiment, components configuring one pixel areallocated to and provided on the first and second semiconductorsubstrates. A signal processing circuit for processing signals suppliedfrom pixels is provided on the second semiconductor substrate.

A first semiconductor substrate 101 includes a first pixel region 103.Photoelectric conversion units are provided like a matrix on the firstpixel region 103. The second semiconductor substrate 102 includes asecond pixel region 104. A part of components included in the pixel areprovided on the second pixel region 104. The second semiconductorsubstrate 102 includes a peripheral circuit 105. The signal processingcircuit for processing signals supplied from pixels is provided on theperipheral circuit region 105. No photoelectric conversion units areprovided on the second pixel region 104 and the peripheral circuitregion 105. The first semiconductor substrate 101 and the secondsemiconductor substrate 102 are provided to face each other acrosswiring for electrically connecting circuits provided on both of thesemiconductor substrates to each other.

Element isolation portions for electrically separating a plurality ofphotoelectric conversion units from one another or from other types ofcomponents of each pixel are provided in the first pixel region 103.Although details will be described below, a feature-part of the presentexemplary embodiment resides in that the element isolation portionsprovided in the first pixel region 103 include no element isolationstructure in which an insulating film is provided in the firstsemiconductor substrate 101.

FIG. 2 illustrates an example of an equivalent circuit of a pixelaccording to the present exemplary embodiment. Although FIG. 2illustrates only one pixel, pixels are actually provided like a matrix.

A pixel 201 includes a photoelectric conversion unit 202, a transferringtransistor 203, a floating diffusion region (hereinafter referred to asFD) 204, an amplifying transistor 205, a resetting transistor 206, and aselecting transistor 207. The photoelectric conversion unit 202 is,e.g., a photodiode. The photoelectric conversion unit 202 performsphotoelectric-conversion of incident light. Generated signal charges canbe stored by the photoelectric conversion unit 202. The transferringtransistor 203 transfers to the FD 204 the signal charges generated inthe photoelectric conversion unit 202. The FD 204 is electricallyconnected to a gate of the amplifying transistor 205. The amplifyingtransistor 205 outputs a signal based on an amount of electric-charge ofthe FD 204. The resetting transistor 206 supplies the FD 204 with avoltage based on a resetting power supply, and resets a voltage of theFD 204. The selecting transistor 207 selects a pixel row from whichsignals are read.

Signals output from the amplifying transistor 205 are output to avertical output line 208. A constant current source 209 is connected tothe vertical output line 208. A source follower circuit is configured toinclude the amplifying transistor 205 and the resetting transistor 206.Each of control lines 210, 211, and 212 is connected to the gates of thetransferring transistor 203, the resetting transistor 206, and theselecting transistor 207.

The photoelectric conversion unit 202, the transferring transistor 203,and the FD 204 are provided in the first pixel region 103 of the firstsemiconductor substrate 101 illustrated in FIG. 1A. The amplifyingtransistor 203, the resetting transistor 206, and the selectingtransistor 207 are provided in the second pixel region 104 of the secondsemiconductor substrate 102 illustrated in FIG. 1A. The second pixelregion 104 is an area differing from the first pixel region 103. Anelectrical connection portion between the first semiconductor substrate101 and the second semiconductor substrate 102 is provided on anelectrical path between the FD 204 and the gate of the amplifyingtransistor 205.

Each pixel according to the present exemplary embodiment includes theselecting transistor. However, the selecting transistor can be omitted.Although a configuration has been illustrated in FIG. 2, in which theselecting transistor 207 is provided on a path between a source of theamplifying transistor 205 and the vertical output line 208, theselecting transistor 207 can be provided on a path between a drain ofthe amplifying transistor 205 and a power supply 209. Alternatively, ananalog-to-digital converter (hereinafter referred to as an ADC) forconverting an analog signal output by the amplifying transistor 205 to adigital signal can be included in the pixel 201.

FIG. 3 illustrates an equivalent circuit of a set of each pixel 201 andthe signal processing circuit according to the present exemplaryembodiment. The pixels 201 illustrated in FIG. 2 are arranged like amatrix. Output nodes of a plurality of pixels 201 included in a singlepixel column are connected to the single vertical output line 208. Asillustrated in FIG. 2, the output nodes of the pixels are the sources ofthe selecting transistors 207. Alternatively, the output nodes of thepixels can be sources of the amplifying transistors 205. A plurality ofvertical output lines 208 are provided respectively corresponding to aplurality of pixel columns. Thus, signals output from a plurality ofpixels 201 included in a single pixel row can be read to a plurality ofvertical output lines 208 in parallel.

A vertical shift register 301 supplies drive pulses to the control lines210, 211, and 212. Respective conduction states of the transferringtransistor 203, the resetting transistor 206, and the selectingtransistor 207 are controlled according to drive pulses supplied by thevertical shift register 301.

A column circuit unit 302 includes a correlated double sampling(hereinafter referred to as CDS) circuit for removing a fixed patternnoise of the pixels, and a column amplifying circuit for amplifyingsignals output from the pixels. The column amplifying circuit is anamplifying circuit configured to include, e.g., an operational amplifierand a feedback capacitor. The column amplifying circuit can be, e.g., avariable-gain amplifying circuit in which a plurality of sets of thefeedback capacitor and a switch connected in series to the feedbackcapacitor are arranged on a feedback path from an output terminal of theoperational amplifier to an input terminal thereof. In addition, thecolumn circuit unit 302 can include a column ADC circuit for converting,into a digital signal, an analog signal corresponding to each column. Itis necessary to provide the column circuit unit 302 only when needarises. A part or the entirety of the column circuit unit 302 can beomitted.

A signal holding unit 303 holds signals output from the pixels. Thesignal holding unit 303 can be configured to hold both of a noise signaland an optical signal onto which the noise signal is superimposed. Thenoise signal includes noise due to an offset of the column amplifyingcircuit of the column circuit unit 302. The optical signal is a signalbased on an amount of signal charge generated by the photoelectricconversion unit 202. The signal holding unit 303 can be configured tohold only optical signals. If the column circuit unit 302 includes acolumn ADC circuit, the signal holding portion 303 can be omitted.

According to drive signals supplied by a horizontal shift register 304,signals held by the signal holding unit 303 are sequentially output,corresponding to each column, to horizontal output lines 305 a and 305b. The signals output to the horizontal output lines 305 a and 305 b aresubjected to difference processing by a difference amplifying unit 306.FIG. 3 illustrates the configuration employing two horizontal outputlines. However, if the signal holding unit is configured to hold onlyoptical signals, a single horizontal output line suffices.

The vertical shift register 301, the column circuit unit 302, the signalholding unit 303, the horizontal shift register 304, and the differenceamplifying unit 306 can be included in the signal processing circuit. Atleast a part or the entirety of the above signal processing circuit isprovided in the peripheral circuit region 105 according to the presentexemplary embodiment.

FIG. 4 is a schematic diagram illustrating a cross-sectional structureincluding the first semiconductor substrate, the second semiconductorsubstrate, and an electrical connection portion between both of thesemiconductor substrates. The first semiconductor substrate 401 includesa first pixel region 403. The second semiconductor substrate 402includes a second pixel region 404 and a peripheral circuit region 405provided with the signal processing circuit.

In the present specification, the term “semiconductor substrate” means alayer of a semiconductor material in which a photoelectric conversionunit and elements such as transistors are formed. In the presentspecification, a structure including semiconductor substrates andmembers made of materials other than semiconductor materials, such asinsulating layers and wiring layers, is referred to simply as asubstrate. If the substrate is a silicon-on-insulator (SOI) substrateconfigured by stacking two layers of semiconductor materials across aninsulating layer provided therebetween, either of the two layers ofsemiconductor materials can be a semiconductor substrate. Alternatively,each semiconductor substrate can be a semiconductor layer formed by anepitaxial growth method. If a specific region is referred to in thefollowing specification, the specific region is distinguished fromsemiconductor substrates, in the following description, by using theterm “semiconductor region”.

In FIG. 4, an upper principal surface of the first semiconductorsubstrate 401 is a first principal surface (hereinafter referred to alsoas a front-side surface) thereof. Wiring electrically connected to agate electrode of the transferring transistor, and to the FD is providedon the first principal surface (i.e., the front-side surface) of thefirst semiconductor substrate 401. A lower principal surface of thefirst semiconductor substrate 401 is a second principal surface(hereinafter referred to also as a back-side surface) thereof. Arrow Lindicates a direction in which light impinges upon the structure. Lightis incident upon the photoelectric conversion portion from the side ofthe second principal surface (i.e., the back-side surface) of the firstsemiconductor substrate 401. A surface (i.e., a lower principal surfaceillustrated in FIG. 4) of the second semiconductor substrate 402, onwhich elements are provided, is a front-side surface thereof.

Sometimes, a principal surface or a front-side surface of asemiconductor substrate is actually an interface between thesemiconductor and an insulating film stacked thereon. More specifically,in the present specification, the term “a front-side surface” or “aprincipal surface” of a semiconductor substrate is not limited to aninterface between a semiconductor substrate and the air or to aninterface between a semiconductor substrate and vacuum.

In the present exemplary embodiment, the first semiconductor substrate401 and the second semiconductor substrate 402 are arranged such thatthe first principal surface (front-side surface) of the firstsemiconductor substrate 401 is directed to the second semiconductorsubstrate 402, and that the front-side surface of the secondsemiconductor substrate is directed to the first semiconductor substrate401. An electrically-conductive pattern including a connection portionwhich will be described below is arranged between the firstsemiconductor substrate 401 and the second semiconductor substrate 402.Thus, the first semiconductor substrate 401 and the second semiconductorsubstrate 402 are arranged to face each other across theelectrically-conductive pattern interposed therebetween.

In the first pixel region 403, the photoelectric conversion portion, theFD, and the transferring transistor are arranged like a matrix in unitsof pixels. That “a transistor is arranged on a semiconductor substrate”means that if the transistor is a metal-oxide semiconductor (MOS)transistor, a semiconductor region configuring a source, and anothersemiconductor region configuring a drain are arranged on a semiconductorsubstrate, and a gate electrode is arranged thereon across an insulatingfilm. The same holds true for a case where a transistor is arranged on asemiconductor region included in a semiconductor substrate.

The photoelectric conversion unit is configured to include an N-typesemiconductor region 406, a P-type semiconductor region 407, and anotherP-type semiconductor region 408. The N-type semiconductor region 406 isa region in which signal charges are collected. The P-type semiconductorregion 407 is arranged in the vicinity of the first principal surface(front-side surface) of the first semiconductor substrate 401 in orderto reduce possibility of mixing of dark current generated on theinterface between the first semiconductor substrate 401 and theinsulating film arranged on the first principal surface (front-sidesurface) side thereof into the signal charges collected in the N-typesemiconductor region 406. The P-type semiconductor region 408 isarranged closer to the second principal surface (back-side surface) ofthe first semiconductor substrate 401 than the N-type semiconductorregion 406. The P-type semiconductor region 408 can be arranged in thevicinity of the first principal surface (front-side surface) of thefirst semiconductor substrate 401 in order to reduce possibility ofmixing of dark current generated on the interface between the firstsemiconductor substrate 401 and the insulating film arranged on thesecond principal surface (back-side surface) side thereof into thesignal charges collected in the N-type semiconductor region 406. EachN-type semiconductor region 406 and each of the associated P-typesemiconductor regions 407 and 408 configure a PN-junction. Thus,embedded type photodiodes are configured.

A transferring gate electrode 409 is arranged across an insulating film(not shown) on the first principal surface (front-side surface) side ina channel region adjoining a photoelectric conversion unit of the firstsemiconductor substrate 401. A channel is formed in the channel regionaccording to a voltage applied to a transferring gate electrode 409. Thechannel region may be made different from the first semiconductorsubstrate 401 in impurity concentration by implantingchannel-impurities, if necessary.

An N-type semiconductor region 410 is arranged adjacent to the channelregion. The N-type semiconductor region 410 configures an FD. The N-typesemiconductor region 410 is higher in impurity concentration than theN-type semiconductor region 406. A transferring transistor is configuredusing the N-type semiconductor region 406, the N-type semiconductorregion 410, and the transferring gate electrode 409 as a source, adrain, and a gate, respectively.

The N-type semiconductor region 410 is connected to wiring across afirst plug 411. The first plug 411 is formed by anelectrically-conductive material such as tungsten. The first plug 411,and the wiring connected to the first plug 411 are arranged on the firstprincipal surface (front-side surface) side of the first semiconductorsubstrate 401.

The amplifying transistor, the resetting transistor, and the selectingtransistor are arranged like a matrix in the second pixel region 404 inunits of pixels. FIG. 4 illustrates a cross-section of the amplifyingtransistor 412 as an example. N-type semiconductor regions serving as asource and a drain of an amplifying transistor 412 are arranged on thesecond semiconductor substrate 402. Preferably, the impurityconcentrations of the N-type semiconductor regions respectively servingas the source and the drain of the amplifying transistor 412 are higherthan that of the N-type semiconductor region 410 configuring the FD. Aninsulating film (not shown) is arranged on the front-side surface of thesecond semiconductor substrate 402. A gate electrode 413 of theamplifying transistor 412 is arranged on the front-side surface of thesecond semiconductor substrate 402 across an insulating film (notshown). The gate electrode 413 of the amplifying transistor 412 isconnected to the wiring across a second plug 414. The second plug 414 isformed by an electrically-conductive material such as tungsten. Thesecond plug 414 connected to a gate of the amplifying transistor 412,and the wiring connected to the second plug 414 are arranged on asurface (front-side surface) side of the second semiconductor substrate402 on which the elements are arranged.

The gate electrode 413 of the transistor arranged in the second pixelregion 404 can be configured such that a polysilicon layer and a metalsilicide layer are stacked. Alternatively, a metal silicide layer can bearranged on a front-side surface of the source regions and the drainregions of the transistors provided in the second pixel region 404.

The N-type semiconductor region 410 configuring the FD, and the gateelectrode 413 of the amplifying transistor 412 are electricallyconnected across a connection portion 415 to each other. The connectionportion 415 is an electrically conductive pattern formed by anelectrically conductive material, e.g., copper. Preferably, a connectionportion connecting the FD and the gate electrode of the amplifyingtransistor is arranged in a region obtained by projecting the firstpixel region 403 in the direction of the second semiconductor substrate402. Preferably, as illustrated in FIG. 4, a plurality of connectionportions are arranged corresponding to the FDs of a plurality of pixels.

Elements configuring the signal processing circuit are arranged in theperipheral circuit region 405 of the second semiconductor substrate 402.FIG. 4 illustrates an element 416 configuring the vertical shiftregister as an example. The vertical shift register supplies drivepulses to wiring 418 arranged on the first principal surface (front-sidesurface) side of the first semiconductor substrate 401 via a connectionportion 417. The wiring 418 is connected to, e.g., a gate of thetransferring transistor. The connection portion 417 is arranged in aregion obtained by projecting the peripheral circuit region 405 in thedirection of the first semiconductor substrate 401. However, theconnection portion 417 can be arranged at another location. A singleconnection portion 417 can be arranged corresponding to a plurality ofpixels included in a single pixel row. Alternatively, a singleconnection portion 417 can be arranged corresponding to each pixel.

In the first pixel region 403, element isolation portions forelectrically isolating pixels from one another, which are arranged likea matrix, are provided in the first pixel region 403. The elementisolation portions isolate the photoelectric conversion portions ofadjacent pixels from one another or isolate the photoelectric conversionportion of each pixel from the FD of each pixel adjacent thereto.Alternatively, the element isolation portions can be configured toisolate the FDs of adjacent pixels from one another.

The present exemplary embodiment uses PN isolation in the elementisolation portions of the first pixel region 403. In a cross-sectionillustrated in FIG. 4, a P-type semiconductor region 419 is providedbetween the photoelectric conversion unit and the N-type semiconductorregion 410 configuring the FD of the adjacent pixel. The P-typesemiconductor region 419 and each of the N-type semiconductor region 406configuring the photoelectric conversion unit, and the N-typesemiconductor region 410 configuring the FD configure a PN-junction. TheP-type semiconductor region 419 serves as a potential barrier.Accordingly, element isolation can be performed by the P-typesemiconductor region 419.

Preferably, a voltage of the P-type semiconductor region 419 is fixed ata GND voltage, and a reverse bias voltage is applied to the PN junction.The P-type semiconductor regions 407, 408, and 419 can be set at thesame voltage by connecting each of the semiconductor regions 407 and 408to the semiconductor region 419. A plurality of contact plugs can beprovided in the first pixel regions 403 as means for supplying apredetermined voltage to each of the P-type semiconductor regions.Alternatively, a single contact plug can be provided in a region otherthan the first pixel region 403. In order to improve the electricalconnection between the contact plug and each of the P-type semiconductorregions 407, 408, and 419, the contact plug can be connected to a P-typesemiconductor region which is provided in the P-type semiconductorregions 407, 408, and 419 and is higher in impurity concentration thanthese regions.

Any element isolation structure can be used in the element isolationportions 420 provided in regions other than the first pixel region 403,i.e., in the second pixel region 404 and the peripheral circuit region405. Preferably, the LOCOS isolation and the STI isolation are used inthe element isolation portions 420. Alternatively, PN isolation andmesa-type insulator isolation can be used in the element isolationportion 420. Preferably, the element isolation portion of the secondpixel region and that of the peripheral circuit region have the sameelement isolation structure. However, the element isolation portion ofthe second pixel region and that of the peripheral circuit region candiffer from each other in element isolation structure.

FIGS. 5A and 5B are schematic diagrams illustrating a planar structureand a cross-sectional structure of each pixel of the first pixel regionin the present exemplary embodiment. FIG. 5A is a schematic diagramillustrating a planar structure of each pixel. FIG. 5B is a schematicdiagram illustrating a cross-sectional structure taken along line A-Billustrated in FIG. 5A. Each component having the same function as thatof an associated component illustrated in FIG. 4 is designated with thesame reference numeral as that designating the associated componentillustrated in FIG. 4. Description of such components is omitted.Associated parts of different pixels are distinguished from one anotherby adding different suffixes to ends of reference numerals.

FIG. 5A illustrates the N-type semiconductor region 406 configuring thephotoelectric conversion unit, the N-type semiconductor region 410configuring the FD, the P-type semiconductor region 419 configuring theelement isolation portion, and the gate electrode 409 of thetransferring transistor. In the present exemplary embodiment, onetransferring transistor and one FD are provided corresponding to onephotoelectric conversion unit. In the present exemplary embodiment, aplurality of transferring transistors and a plurality of FDs arearranged like a matrix in units of pixels. More specifically, the firstpixel region is divided into domains and in each domain, each of aplurality of pixels is provided. Thus, in each of the divided domains, aphotoelectric conversion unit, a transistor and an FD included in anassociated single pixel are provided.

The P-type semiconductor region 419 is provided such that a plurality ofpixels provided in the first pixel region can electrically be isolatedfrom one another. More specifically, the P-type semiconductor region 419is provided between an N-type semiconductor region 406 a of each pixeland an N-type semiconductor region 406 b of each pixel adjacent thereto,and between an N-type semiconductor region 410 a of each pixel and anN-type semiconductor region 406 c of each pixel adjacent thereto. Inaddition, the P-type semiconductor region 419 is provided between theN-type semiconductor region 410 a of each pixel and an N-typesemiconductor region 410 b of each pixel adjacent thereto.

Each region 501 surrounded by dashed lines illustrated in FIG. 5Aindicates an area in which P-type semiconductor regions 407 are notprovided. The P-type semiconductor regions 407 are provided in theentire area other than the regions 501. More specifically, the P-typesemiconductor region 407 extends over a plurality of pixels. The P-typesemiconductor region 407 is higher than the P-type semiconductor region419 in impurity concentration.

As illustrated in FIG. 5A, in the present exemplary embodiment, theN-type semiconductor regions 410 and the P-type semiconductor region 407are provided at a predetermined distance in a direction along a plane ofa plan diagram. An end part along a channel direction of thetransferring gate 409 of each transferring transistor coincides withthat of the P-type semiconductor region 407. According to such anarrangement, the P-type semiconductor 407 defines a channel width of thetransferring transistor even when an end part of the P-typesemiconductor region 407 is located at a lower part of the transferringgate electrode 409.

The arrangement of the P-type semiconductor region 407 is not limited tothat. As long as the P-type semiconductor region 407 is provided on atleast a part of the N-type semiconductor region 406, the arrangement canbe employed.

In order to miniaturize the pixels, it is desirable that the center ofgravity of the N-type semiconductor region 410 a configuring the FD ofeach pixel and that of gravity of the N-type semiconductor region 410 bconfiguring the FD of a pixel adjacent thereto are spaced at a distanceequal to or less than 3 micrometers.

FIG. 5B further illustrates the P-type semiconductor region 408, thefirst plug 411, an insulating film provided on the first principalsurface (front-side surface) side of the first semiconductor substrate401, and an insulating film 503 provided on the second principal surface(back-side surface) side thereof. Although FIG. 5B illustrates aconfiguration in which the P-type semiconductor region 407 is providedonly on the first principal surface side of the N-type semiconductorregion 406, the P-type semiconductor region 407 can be provided on anarea in which the element isolation region 419 is provided.

A P-type semiconductor region 504 can be provided under the N-typesemiconductor region 410 configuring the FD. It is desirable that theP-type semiconductor region 504 is arranged to extend in the directionof the plane of the plan diagram over the entire surface of the region501 surrounded by the dashed lines. More specifically, it is desirablethat when the P-type semiconductor region 409 and the P-typesemiconductor region 504 are projected in the direction of theinsulating film 502, an area onto which the P-type semiconductor region409 is projected does not overlap with an area onto which the P-typesemiconductor region 504 is projected.

An amount of electric-charges of the N-type semiconductor regions 406,which are mixed into those of the N-type semiconductor regions 410, canbe reduced by the P-type semiconductor region 504. During an exposuretime period, a negative voltage is applied to the transferring gateelectrode 407. Thus, a potential barrier for electrons in thesemiconductor region provided under the transferring gate electrode 407is increased. However, an electric field from the transferring gateelectrode 407 does not sufficiently reach the inside of thesemiconductor substrate. Accordingly, the potential barrier between theN-type semiconductor regions 406 and 410 is low. It is favorable thatthe P-type semiconductor region 504 is provided in a region which anelectric field from the transferring gate electrode 407 does notsufficiently reach, in the semiconductor substrate.

As illustrated in FIG. 5B, a depth of the interface between the firstsemiconductor substrate 401 and the insulating film 502 in the elementisolation portion with respect to the interface therebetween in thephotoelectric conversion unit is 0. If the SIT isolation or the LOCOSisolation is applied to the second pixel region or the peripheralcircuit region, the depth of the interface between the firstsemiconductor substrate 401 and the insulating film 502 in the elementisolation portion is shallower than that of the interface between thefirst semiconductor substrate 401 and a insulating film in such anelement isolation portion due to the SIT isolation or the LOCOSisolation.

The present exemplary embodiment doesn't use an element isolationstructure in which an insulating film is provided in the semiconductorsubstrate, in each element isolation portion due to the LOCOS isolationor the STI isolation in the first pixel region. The structure in whichan insulating film is provided in the semiconductor substrate includes astructure in which the insulating film stacked in the semiconductorsubstrate has a part protruding in a direction of the semiconductorsubstrate. However, the element isolation portion of the first pixelregion doesn't include an element isolation structure in which theinsulating film is provided in the semiconductor substrate. Thus, theinterface between the first semiconductor substrate 401 and theinsulating film 502 provided in the first principal surface (front-sidesurface) side of the first semiconductor substrate 401 extends flat overthe first pixel region. It is not necessary that the interface betweenthe semiconductor substrate and the insulating film (hereinaftersometimes referred to as a semiconductor-substrate/insulating-filminterface) is completely flat. For example, asemiconductor-substrate/insulating-film interface can have roughness dueto a manufacturing process.

The element isolation structure due to the above PN isolation is anelement isolation structure due to the semiconductor region serving as apotential barrier for signal charges. Thus, thesemiconductor-substrate/insulating-film interface extends substantiallyflat. A structure in which the insulating film is locally thick due tothe LOCOS isolation falls under the category of the structure in whichthe insulating film is provided in the semiconductor substrate.

A structure in which the insulating film is embedded into a grooveformed in the semiconductor substrate for the STI isolation, falls underthe category of the structure in which the insulating film is providedin the semiconductor substrate. Accordingly, if the LOCOS isolation orthe STI isolation is used in the element isolation portion, theinterface between the semiconductor substrate and the insulating film isnot flat.

If the insulating film is provided in the semiconductor substrate,stress is generated in the semiconductor substrate. Thus, interfacedefect increases, as compared with a case where the interface betweenthe semiconductor substrate and the insulating film is substantiallyflat. When the interface defect increases, dark current increases.Accordingly, if the interface between the semiconductor substrate andthe insulating film is substantially flat, the possibility of occurrenceof dark current can be reduced, as compared with the case where theinterface therebetween is not flat.

According to the present exemplary embodiment, a (1 0 0)-surface of thesemiconductor substrate can be set to be the first principal surface(front-side surface). Generally, when an insulating film is provided onthe (1 0 0)-surface of the semiconductor substrate, there is anadvantage that interface defect is reduced, as compared with the casewhere the insulating film is provided on another surface. If theinterface therebetween is not flat in the configuration in which the (10 0)-surface of the semiconductor substrate is set to be the firstprincipal surface, the semiconductor-substrate/insulating-film interfaceis provided on the surface other than the (1 0 0)-surface. Accordingly,the interface defect increases and the dark current increases.

As described above, in the present exemplary embodiment, thephotoelectric conversion unit, the transferring transistor, and the FDare provided in the first pixel region, while the amplifying transistor,and the resetting transistor are provided in another pixel region, i.e.,the second pixel region. The element isolation portion of the firstpixel region doesn't include an element isolation structure in which aninsulating film is provided in the first semiconductor substrate. Thus,the interface between the semiconductor region of the firstsemiconductor substrate and the insulating film stacked in thefront-side surface of the first semiconductor substrate is substantiallyflat over the first pixel region.

With such a configuration, mixing of noise due to dark current generatedon the interface between the semiconductor substrate and the insulatingfilm for isolating the amplifying transistor and the resettingtransistor, into the photoelectric conversion unit can be reduced. Inaddition, with such a configuration, a wide element isolation portion isnot needed in the first pixel region. Thus, a rate of the photoelectricconversion unit to a planar size of each pixel can be increased.Accordingly, enhancement of sensitivity of each pixel andminiaturization thereof can be achieved.

According to the configuration of the present exemplary embodiment,noise due to color mixture among pixels can be reduced. Light rays whichare incident from the second principal surface (back-side surface) ofthe first semiconductor substrate and unabsorbed by the substrate, reachthe interface between the semiconductor region of the firstsemiconductor substrate and the insulating film stacked on the firstprincipal surface (front-side surface) side of the semiconductor region.A part of light reaching the interface is deflected or reflected by theinterface between the semiconductor substrate and the insulating film.If the region provided with the photoelectric conversion unit includesthe element isolation structure in which the insulating film is providedin the first semiconductor substrate, such light is irregularlyreflected because of a complex shape of the insulating film. Arelatively large amount of light goes into an adjacent pixel. Such lightcauses mixed color. In the present exemplary embodiment, the interfacebetween the semiconductor region and the insulating film in the firstpixel region is substantially flat. Therefore, irregular reflection ofincident light on the first principal surface (front-side surface) ofthe first semiconductor substrate can be reduced. Consequently,occurrence of color mixture among adjacent pixels can be reduced.

In the first exemplary embodiment, a configuration using the PNisolation in the element isolation portion of the first pixel region isdescribed as an example. Hereinafter, a modification of the firstexemplary embodiment is described. The mesa-type insulator isolation canbe used in the element isolation portion of the first pixel region. FIG.12 is a schematic diagram illustrating a cross-sectional structure of amesa-type insulator isolation portion.

An insulating film provided on the first principal surface (front-sidesurface) of the first semiconductor substrate 401 has a protrusionportion 1201 provided on a side opposite to the first semiconductorsubstrate. The protrusion portion 1201 can be configured by either apart of the insulating film provided on the first principal surface ofthe first semiconductor substrate 401 or a member differing from theinsulating film. Alternatively, the protrusion portion 1201 can beconfigured by stacking an insulating film on another insulating filmprovided on the first principal surface of the first semiconductorsubstrate 401. A P-type semiconductor region 1202 is provided in aregion in which the protrusion portion 1201 is provided on the firstprincipal surface (front-sided surface) side of the first semiconductorsubstrate 401. A transferring gate 1202 of the transferring transistorcan be provided on the protrusion portion 1201.

Thus, even when the mesa-type insulator isolation is used, a thickinsulating film is provided, similarly to the case of using the LOCOSisolation. However, even in the case of using the mesa-type insulatorinsulation, the interface between the first semiconductor substrate 401and the insulating film provided on the first principal surface(front-side surface) side of the first semiconductor substrate 401extends substantially flat over the first pixel region. Accordingly,stress generated in the semiconductor substrate is small, differentlyfrom the case of using the LOCOS isolation. Thus, advantages similar tothose of the first exemplary embodiment can be obtained.

In order to improve the function of element isolation, the elementisolation structure in which an insulating film is provided in thesemiconductor substrate can be used in the element isolation portion ofthe first pixel region. However, it is desirable that an amount ofprotrusion of the insulating film into the semiconductor substrate issmall, as compared with the element isolation portion provided in thesecond pixel region or the peripheral circuit region.

FIG. 12B is a schematic diagram illustrating a cross-sectional structureof each pixel in the first pixel region according to a modification ofthe first exemplary embodiment. However, description of a part thereof,which is similar to that illustrated in FIG. 5B, is omitted. FIG. 12C isa schematic diagram illustrating a cross-sectional structure of thesecond pixel region or the peripheral circuit region.

As illustrated in FIG. 12B, an insulating film provided on the firstprincipal surface (front-side surface) of the first semiconductorsubstrate 401 protrudes into the first semiconductor substrate 401 inthe element isolation portion. More specifically, an interface 1204between the first semiconductor substrate 401 and an insulating film inthe element isolation portion is provided at a first depth 1206 withrespect to an interface 1204 between the first semiconductor substrate401 and an insulating film in the photoelectric conversion unit. AP-type semiconductor region 1207 is provided in the element isolationportion of the first pixel region. A practical example of such aconfiguration is a structure due to electro-deionization (EDI)isolation. The structure due to the EDI isolation is configured toinclude a P-type semiconductor region and an insulating film depositedon an upper part of the P-type semiconductor region.

A depth direction is defined as a direction perpendicular to the firstprincipal surface (front-side surface) in the photoelectric conversionunit of the first semiconductor substrate. That the “depth is shallow”means that a distance from a reference surface is small.

FIG. 12C is a schematic diagram illustrating a cross-sectional structureof a transistor provided in the second pixel region or the peripheralcircuit region. An example of a configuration using the STI isolationfor the element isolation of the second pixel region or the peripheralcircuit region is described hereinafter. However, the configuration canuse the LOCOS isolation.

N-type semiconductor regions 1208 and 1209 respectively configuring asource or a drain of a transistor are provided on the front-side surfaceof the second semiconductor substrate 402. A gate electrode 1201 isprovided on the front-side surface side of the second semiconductorsubstrate 402 across an insulating film.

A P-type semiconductor region 1214 is provided in the element isolationportion of the second semiconductor substrate 402. A groove is providedin the element isolation portion of the second semiconductor substrate402. An insulating film is embedded in the groove. Thus, the insulatingfilm provided on the front-side surface of the second semiconductorsubstrate 402 protrudes into the second semiconductor substrate 402 inthe element isolation portion. More specifically, an interface 1212between the second semiconductor substrate 402 and the insulating filmin the element isolation portion is provided at a second depth 1213 withrespect to an interface 1211 between the second semiconductor substrate402 and the insulating film in a region in which a transistor isprovided. The region serving as a reference, in which a transistor isprovided, is, e.g., a semiconductor region configuring the source ordrain of the transistor.

The present exemplary modification has a feature that the first depth1206 is shallow, as compared with the second depth 1213. The presentexemplary modification can be applied to a case where the first depth1206 is zero, in other words where the interface between the firstsemiconductor substrate 401 and the insulating film is substantiallyflat.

If the element isolation portion of the first pixel region includes theinsulating film provided in the semiconductor substrate, increase ofdark current is small in case where an amount of protrusion of theinsulating film into the semiconductor substrate is small, as comparedwith the element isolation portions of other regions. Accordingly,advantages substantially the same as those of the first exemplaryembodiment can be obtained.

In the case of the present modification, the second pixel regionincluded in the second semiconductor substrate, or the element isolationportion provided in the peripheral circuit region is employed as atarget of comparison. As described below, a configuration including aperipheral circuit region provided in the semiconductor substrate can beemployed. In addition, an element isolation portion provided in theperipheral circuit region included in the first semiconductor substratecan be employed as a target of comparison.

Next, a suitable manufacturing method for manufacturing the solid-stateimaging device according to the first exemplary embodiment is brieflydescribed hereinafter with reference to the drawings. FIG. 13A through13C is a schematic diagram illustrating a cross-sectional structure in amanufacturing process according to the first exemplary embodiment.

FIG. 13A illustrates a step of preparing the first semiconductorsubstrate 401. The first semiconductor substrate 401 is, e.g., a siliconsubstrate. An element isolation portion is formed in the first pixelregion of the first semiconductor substrate 401. Then, eachsemiconductor region and a gate electrode are formed in and on the firstsemiconductor substrate 401. Next, a plurality of interlayer insulatingfilms and second multilayer wiring 1301, in which a plurality of wiringlayers are stacked, are formed on the first principal surface(front-side surface) side of the first semiconductor substrate 401. Aplurality of wiring layers is connected by contact plugs to one another.A connection portion 1302 to be connected to the first semiconductorsubstrate 401 is provided on the uppermost layer of the first multilayerwiring layer 1301.

FIG. 13B illustrates a step of preparing the second semiconductorsubstrate 402. The second semiconductor substrate 402 is, e.g., asilicon substrate. A second pixel region and an element isolationportion are formed in the second semiconductor substrate and theperipheral circuit region. Then, each semiconductor region and a gateelectrode are formed in and on the second semiconductor substrate 402.Next, a plurality of interlayer insulating films and second multilayerwiring 1303, in which a plurality of wiring layers are stacked, areformed on the front-side surface side of the second semiconductorsubstrate 402. A plurality of wiring layers is connected by contactplugs to one another. A connection portion 1304 to be connected to thefirst semiconductor substrate 401 is provided on the uppermost layer ofthe second multilayer wiring layer 1303.

FIG. 13C illustrates a step of connecting the first semiconductorsubstrate 401 to the second semiconductor substrate 402. The connectionportion 1302 illustrated in FIG. 13A, and the connection portion 1304illustrated in FIG. 13B are connected to associated connection parts,respectively. As a suffix of the associated connection part, the samealphabetic character is added as that of the connection portion. Forexample, a connection portion 1302 illustrated in FIG. 13A is connectedto a connection part 1304 a illustrated in FIG. 13B.

As illustrated in FIG. 13C, the first semiconductor substrate 401 andthe second semiconductor substrate 402 are provided such that the firstprincipal surface (front-side surface) of the first semiconductorsubstrate 401 faces the second semiconductor substrate 402, and that thefront-side surface of the second semiconductor substrate 402 faces thefirst semiconductor substrate 401.

After the process of connecting the first semiconductor substrate 401 tothe second semiconductor substrate 402, an optical member 1305 is formedon the second principal surface (back-side surface) opposite to thefirst principal surface of the first semiconductor substrate 401, ifnecessary. The optical member 1305 can include a light shielding film, acolor filter, and a microlens.

A silicon dioxide film, a silicon nitride film, a silicon oxynitridefilm, and a film stack of such films can be used as the insulating filmaccording to the present exemplary embodiment. In the followingdescription of a second exemplary embodiment or later, examples using asilicon dioxide film as the insulating film are described.

Hereinafter, a second embodiment of the solid-state imaging device towhich the present invention is applied is described. In the presentexemplary embodiment, the first semiconductor substrate 101 and thesecond semiconductor substrate 102 are arranged to face each otheracross wiring for connecting circuits provided on both of thesemiconductor substrates 101 and 102, similarly to those of the firstexemplary embodiment. A feature of the second exemplary embodiment isthat a plurality of pixels share an FD. A detailed description ofcomponents of the present exemplary embodiment, which are similar toassociated components of the first exemplary embodiment, is omitted.

FIG. 6 is an equivalent circuit diagram illustrating an equivalentcircuit of each pixel according to the present exemplary embodiment.Each component of the present exemplary embodiment, which has the samefunction as that of an associated component illustrated in FIG. 2, isdesignated with the same reference numeral as that denoting theassociated component. Thus, a detailed description of such components isomitted. In the present exemplary embodiment, a first photoelectricconversion unit 601 a, a second photoelectric conversion unit 601 b, afirst transferring transistor 602 a, a second transferring transistor602 b, and an FD 603 are provided. The first photoelectric conversionunit 601 a is connected to the FD 603 via the first transferringtransistor 602 a. The second photoelectric conversion unit 601 b isconnected to the FD 603 via the second transferring transistor 602 b.More specifically, a pixel including the first photoelectric conversionunit 601 a and another pixel including the second photoelectricconversion unit 601 b share the FD 603. A control line 604 a and anothercontrol line 604 b are connected to a gate of the first transferringtransistor 602 a and that of the second transferring transistor 602 b,respectively.

The first photoelectric conversion unit 601 a, the second photoelectricconversion unit 601 b, the first transferring transistor 602 a, thesecond transferring transistor 602 b, and the FD 603 are provided in thefirst pixel region 103 of the first semiconductor substrate 101illustrated in FIG. 1A. The amplifying transistor 205, the resettingtransistor 206, and the selecting transistor 207 are provided in thesecond pixel region 104 of the second semiconductor substrate 102illustrated in FIG. 1A. The electrical connection portion between thefirst semiconductor substrate 101 and the second semiconductor substrate102 is provided on the path between the FD 603 and the gate of theamplifying transistor 205.

FIG. 6 illustrates a single unit 600 including two pixels that share theFD 603. Actually, a plurality of units 600 are arranged like a matrix. Aplurality of units 600 included in a single column is connected to thevertical output line 208.

In the present exemplary embodiment, the PN isolation is used in theelement isolation portion of the first pixel region. Accordingly, theinterface between the first semiconductor substrate 101 and theinsulating film stacked on the first principal surface (front-sidesurface) side thereof extends substantially flat over the first pixelregion.

FIG. 7 is a schematic diagram illustrating a planar structure of eachpixel in the first pixel region in the present exemplary embodiment.FIG. 7 illustrates an N-type semiconductor region 701 configuring thephotoelectric conversion unit, a transferring gate electrode 702 of thetransferring transistor, and an N-type semiconductor region 703configuring the FD. Associated components of different pixels aredistinguished from one another by adding different suffixes to ends ofreference numerals.

A set of an N-type semiconductor region 701 a and a transferring gateelectrode 702 a, and a set of an N-type semiconductor region 701 b and atransferring gate electrode 702 b are provided corresponding to anN-type semiconductor region 703 a. Signal charges generated by theN-type semiconductor regions 701 a and 701 b are transferred by thetransferring gate electrodes 702 a and 702 b to the N-type semiconductorregion 703 a serving as the FD. Thus, a plurality of pixels shares theFD. Even in the present exemplary embodiment, element isolation portions(not shown) for electrically isolating a plurality of pixels provided inthe first pixel region from one another are provided.

The solid-state imaging device according to the present exemplaryembodiment has the following advantage in addition to those of the firstexemplary embodiment. According to the present exemplary embodiment, aplurality of the pixels shares the FD. With such a configuration, thenumber of elements configuring each pixel can be reduced. Thus, a rateof the photoelectric conversion unit to the planar size of pixels can befurther increased. Accordingly, further enhancement of sensitivity ofeach pixel and further miniaturization thereof can be achieved.

The number of pixels sharing the FD is not limited to 2. Three or morepixels can share the FD. FIG. 8 illustrates a planar structure of eachpixel of the first pixel region in a modification of the presentexemplary embodiment. In the modification, four N-type semiconductorregions 801 a, 801 b, 801 c, and 801 d are respectively connected viatransferring gate electrodes 802 a, 802 b, 802 c, and 802 d oftransferring transistors to an N-type semiconductor region 803configuring an FD.

With the configuration in which such four pixels share a common FD,further enhancement of the sensitivity of each pixel, or furtherminiaturization thereof can be achieved, as compared with theconfiguration in which two pixels share the common FD.

In the present exemplary embodiment, a configuration similarly to thatof the modification of the first exemplary embodiment can be applied tothe device. For example, the mesa-type insulator isolation can be usedin the element isolation portions of the first pixel region. Inaddition, the element isolation structure, in which an insulating filmdue to the EDI isolation or the like is provided in the semiconductorsubstrate, can be used in the element isolation portions of the firstpixel region.

Next, a third exemplary embodiment of the solid-state imaging device towhich the present invention is applied is described. In the presentexemplary embodiment, the first semiconductor substrate 101 and thesecond semiconductor substrate 102 are provided across wiring forconnecting circuits provided on both of the semiconductor substrates 101and 102 to face each other. A feature-part of the third exemplaryembodiment is that the first semiconductor substrate includes a firstperipheral circuit region in which a part of the signal processingcircuit is provided at a location other than the first pixel region inwhich the photoelectric conversion unit is provided. A detaileddescription of components of the present exemplary embodiment, which aresimilar to associated components of the first exemplary embodiment, isomitted.

FIG. 1B is a schematic diagram illustrating a planar structure of thefirst semiconductor substrate and the second semiconductor substrateincluded in the solid-state imaging device according to the presentexemplary embodiment. A first semiconductor substrate 111 includes afirst pixel region 113 and a first peripheral circuit region 114. Asecond semiconductor substrate 112 includes a second pixel region 115and a second peripheral circuit region 116. No photoelectric conversionunits are provided in the first peripheral circuit region 114, thesecond pixel region 115, and the peripheral circuit region 116. Nophotoelectric conversion units are provided in the second pixel region104 and the peripheral circuit region 105. The first semiconductorsubstrate 101 and the second semiconductor substrate 102 are providedacross wiring for connecting the circuits provided on both of thesemiconductor substrates to face each other.

FIG. 9 illustrates a schematic diagram illustrating a cross-sectionalstructure including the first semiconductor substrate, the secondsemiconductor substrate, and an electrical connection portion betweenboth of the semiconductor substrates in the solid-state imaging deviceaccording to the present exemplary embodiment. A first semiconductorsubstrate 901 includes a first pixel region 903 and a first peripheralcircuit region 904. A second semiconductor substrate 902 includes asecond pixel region 905 and a second peripheral circuit region 906.

In FIG. 9, an upper principal surface of the first semiconductorsubstrate 901 is a first principal surface (front-side surface). A gateelectrode of the transferring transistor, and wiring connected to an FDare provided on the first principal surface (front-side surface) side ofthe first semiconductor substrate 901. A lower principal surface of thefirst semiconductor substrate 901 is a second principal surface(back-side surface). Arrow L indicates a direction in which light isincident. As indicated by arrow L, light is incident on thephotoelectric conversion unit from a second principal surface (back-sidesurface) side of the first semiconductor substrate 901. A surface (lowerprincipal surface illustrated in FIG. 9) of the second semiconductorsubstrate 902, on which elements are provided, is a front-side surfaceof the second semiconductor substrate 902.

In the present exemplary embodiment, the first semiconductor substrate401 and the second semiconductor substrate 402 are arranged such thatthe first principal surface (front-side surface) of the firstsemiconductor substrate 401 faces the second semiconductor substrate402, and that the front-side surface of the second semiconductorsubstrate 402 faces the first semiconductor substrate 401. Anelectrically-conductive pattern including a connection portion (to bedescribed below) is provided between the first semiconductor substrate401 and the second semiconductor substrate 402. Thus, the firstsemiconductor substrate 401 and the second semiconductor substrate 402are arranged across the electrically-conductive pattern to face eachother.

In the first pixel region 903, the photoelectric conversion units, theFDs, and the transferring transistors are arranged like a matrix inunits of pixels. In the second pixel region 905, the amplifyingtransistors and the resetting transistors are arranged like a matrix inunits of pixels. FIG. 9 illustrates a cross-section of the amplifyingtransistor as an example. An N-type semiconductor region 907 configuringan FD, and a gate electrode 908 of the amplifying transistor areelectrically connected via a connection portion 909 to each other.

In the present embodiment, a part of elements configuring a signalprocessing circuit is provided in the first peripheral circuit region904, while another part of the elements is provided in the secondperipheral circuit region 906. It is suitable that a circuit 910 forsupplying drive pulses to the gate of the transferring transistor, whichis included in the vertical shift register, is provided in the firstperipheral circuit region 904. Elements provided in the first peripheralcircuit region 904 are electrically connected to those provided in thesecond peripheral circuit region 906 via, e.g., a connection portion911.

Element isolation portions for electrically isolating pixels arrangedlike a matrix are provided in the first pixel region 903. Each elementisolation portion isolates the photoelectric conversion units of pixelsadjoining each other. Alternatively, each element isolation portionisolates the photoelectric conversion unit of a pixel from an FD ofanother pixel adjacent thereto. Alternatively, the element isolationportion can be configured to isolate FDs of pixels adjoining oneanother.

In the present exemplary embodiment, the PN isolation is used in theelement isolation portions of the first pixel region 903. The P-typesemiconductor region 419 is provided between the photoelectricconversion unit and the N-type semiconductor region 907 configuring theFD of the pixel adjacent thereto. The P-type semiconductor region 419serves as a potential barrier for electrons in the N-type semiconductorregion. Thus, the P-type semiconductor region 419 can achieve elementisolation.

Any element isolation structure can be used in regions other than thefirst pixel region 903, i.e., in the first peripheral circuit region904, the second pixel region 905, and the second peripheral circuitregion 906. Preferably, the LOCOS isolation and the STI isolation areused. Alternatively, the PN isolation or the mesa-type insulatorisolation can be used. Preferably, an element isolation portion 913 a ofthe first peripheral circuit region, an element isolation portion 913 bof the second pixel region, and an element isolation portion 913 c ofthe second peripheral circuit region have the same element isolationstructure. However, the element isolation portions 913 a, 913 b, and 913c can differ from one another in element isolation structure.

In the present exemplary embodiment, a configuration similar to thataccording to the modification of the first exemplary embodiment can beapplied to the device. The mesa-type insulator isolation can be used inthe element isolation portions of the first pixel region. An elementisolation structure in which an insulating film is provided in thesemiconductor substrate can be used in the element isolation portions ofthe first pixel region.

The present exemplary embodiment has the following advantages inaddition to those of the first exemplary embodiment. According to thethird exemplary embodiment, the first semiconductor substrate includesthe first peripheral circuit region at a location differing from that ofthe first pixel region. In addition, a part of elements configuring asignal processing circuit are provided in the first peripheral circuitregion. With such a configuration, the area of the second peripheralcircuit region provided in the second semiconductor substrate can bereduced. Thus, the area of the solid-state imaging device, i.e., a chiparea can be reduced.

Next, a fourth exemplary embodiment of the solid-state imaging device towhich the present invention is applied is described. A feature-part ofthe present exemplary embodiment is that one semiconductor substrateincludes a first pixel region in which photoelectric conversion portionsare provided, and that a second pixel region and a peripheral circuitregion are included at a place differing from the first pixel region.Description of components of the present exemplary embodiment, which aresimilar to associated components of the first through third exemplaryembodiments, is omitted.

FIG. 1C is a schematic diagram illustrating a planar structure of asemiconductor substrate included in the solid-state imaging deviceaccording to the present exemplary embodiment. A semiconductor substrate121 includes a first pixel region 122, a second pixel region 123, and aperipheral circuit region 124. Photoelectric conversion units areprovided in the first pixel region 122. No photoelectric conversionunits are provided in the second pixel region 123 and the peripheralcircuit region 124.

FIG. 10 is an equivalent circuit diagram illustrating an equivalentcircuit of each pixel according to the present exemplary embodiment.FIG. 10 illustrates six pixels arranged like a matrix with two rows andthree columns. However, the number of pixels included in the solid-stateimaging device according to the present exemplary embodiment is notlimited thereto.

A pixel 1001 includes a photoelectric conversion unit 1002, atransferring transistor 1003, and an FD 1004. An amplifying transistor1005 and a resetting transistor 1006 are provided in each image column.

FDs 1004 of a plurality of pixels included in a single pixel column areconnected to one another, and to a gate of the amplifying transistor1005. A drain of the amplifying transistor 1005 is connected to a powersupply. A source of the amplifying transistor 1005 is connected to avertical output line 1007. A drain of the resetting transistor 1006 isconnected to the power supply. A source of the resetting transistor 1006is connected to the FD 1004. A constant current source 1008 is connectedto the vertical output line 1007. The amplifying transistor 1005 and theconstant current source 1008 connected thereto configure a sourcefollower circuit. A control line 1010 is connected to a transferringtransistor 1002. A control line 1010 is connected to the gate of theresetting transistor 1006. A signal processing circuit (not shown) isprovided at a subsequent stage of the vertical output line 1007.

In the present embodiment, elements surrounded by dashed lines 1001 areprovided in the first pixel region 122 illustrated in FIG. 1C. Elementssurrounded by dashed lines 1012 are provided in the second pixel region123 illustrated in FIG. 1C. Thus, no transistors other than thetransferring transistor 1003 are provided in the first pixel region 122in which a plurality of photoelectric conversion portions are arranged.The amplifying transistors 1005 and the resetting transistors 1006 areprovided in the second pixel region 123 other than the first pixelregion 122 in which a plurality of photoelectric conversion units arearranged.

FIG. 11 is a schematic diagram illustrating a cross-sectional structureof the semiconductor substrate in the sold-state imaging deviceaccording to the present exemplary embodiment. A semiconductor substrate1101 includes a first pixel region 1102, a second pixel region 1103, anda peripheral circuit region 1104.

In FIG. 11, a principal surface on a side (upper side as viewed in FIG.11), on which wiring of the semiconductor substrate 1101 is provided, isa first principal surface (front-side surface). Arrow L indicates adirection in which light is incident. As indicated by arrow L, light isincident from a second principal surface (back-side surface) opposite tothe first principal surface (front-side surface) of the semiconductorsubstrate 1101.

Photoelectric conversion units, FDs, and transferring transistors areprovided in the first pixel region 1102. In the second pixel region1103, the amplifying transistors 106 and the resetting transistors 107are provided. FDs of a plurality of pixels included in a single pixelcolumn are connected to common wiring 1105. The common wiring 1105 isconnected to a gate electrode of the amplifying transistor 1106. Asource of the resetting transistor 1107 is connected to the commonwiring 1105. Elements configuring a signal processing circuit areprovided in the peripheral circuit region 1104.

Element isolation portions for electrically isolating a plurality ofpixels arranged like a matrix from one another are provided in the firstpixel region 1102. Each element isolation portion isolates thephotoelectric conversion units of pixels adjoining each other.Alternatively, each element isolation portion isolates the photoelectricconversion unit of a pixel from an FD of another pixel adjacent thereto.Alternatively, the element isolation portion can be configured toisolate FDs of pixels adjoining one another.

The PN isolation is used in the element isolation portions of the firstpixel region 1102. The P-type semiconductor region 1108 is providedbetween the photoelectric conversion unit and the FD of the pixeladjacent thereto in the cross-section illustrated in FIG. 11. The P-typesemiconductor region 1108 serves as a potential barrier for electrons inthe N-type semiconductor region. Thus, the P-type semiconductor region1108 can achieve element isolation.

Any element isolation structure can be used in regions other than thefirst pixel region 1102, i.e., in the element isolation portions 1109provided in the second pixel region 1103, and the peripheral circuitregion 1104. Preferably, the LOCOS isolation and the STI isolation areused. Alternatively, the PN isolation or the mesa-type insulatorisolation can be used. Preferably, an element isolation portion 1109 aof the second pixel region, and an element isolation portion 1109 b ofthe peripheral circuit region have the same element isolation structure.However, the element isolation portions 1109 a and 1109 b can differfrom one another in element isolation structure.

In the present exemplary embodiment, a configuration similar to thataccording to the modification of the first exemplary embodiment can beapplied to the device. The PN isolation and the mesa-type insulatorisolation can be used therein. An element isolation structure in whichan insulating film is provided in the semiconductor substrate can beused in the element isolation portions of the first pixel region.

The present exemplary embodiment has the following advantages inaddition to those of the first exemplary embodiment. According to thefourth exemplary embodiment, one semiconductor substrate includes thefirst pixel region in which the photoelectric conversion units areprovided, and the second pixel region and the peripheral circuit region,which are located at places differing from the first pixel region. Inaddition, an element isolation structure in which an insulating film isprovided in the semiconductor substrate is not used in the first pixelregion. With such a configuration, in the process of manufacturing thesolid-state imaging device, a step of arranging two semiconductorsubstrates to face each other, and connecting the two semiconductorsubstrates is unnecessary. Consequently, the process of manufacturingthe solid-state imaging device can be simplified.

In the above first through fourth exemplary embodiments, the back-sidesurface irradiation type solid-state imaging device has been describedas an example. However, the present invention can be applied to afront-side surface irradiation type solid-state imaging device.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all modifications, equivalent structures, and functions.

This application claims priority from Japanese Patent Application No.2010-149476 filed Jun. 30, 2010, which is hereby incorporated byreference herein in its entirety.

The invention claimed is:
 1. A solid-state imaging device comprising aplurality of pixels, each including: a photoelectric conversion unit; afloating diffusion region; a transferring transistor including atransferring gate electrode configured to transfer signal chargegenerated at the photoelectric conversion unit to the floating diffusionregion; an amplifying transistor configured to output a signal based onan amount of electric charge of the floating diffusion region; and aresetting transistor configured to reset a voltage of the floatingdiffusion region, the solid-state imaging device further comprising; afirst semiconductor substrate and a second semiconductor substrate,wherein a first insulating film is provided on a first principal surfaceof the first semiconductor substrate, wherein the first semiconductorsubstrate includes a first pixel region; wherein a plurality ofphotoelectric conversion units and a plurality of floating diffusionregions are arranged in the first pixel region; wherein a first elementisolation portion is provided in the first pixel region, configured toelectrically isolate at least a part of the plurality of photoelectricconversion units and at least a part of the plurality of floatingdiffusion regions from each other; wherein a second insulating film isprovided on the second semiconductor substrate; wherein the secondsemiconductor substrate includes a second pixel region; wherein aplurality of the amplifying transistors and a plurality of the resettingtransistors are arranged in the second pixel region; wherein a secondelement isolation portion is provided in the second pixel region,configured to electrically isolate at least a part of the plurality ofthe amplifying transistors and at least a part of the plurality of theresetting transistors from each other; wherein an interface of a regionwhere the first element isolation portion is provided, between the firstsemiconductor substrate and the first insulating film, is arranged at afirst depth with respect to an interface of a region where thephotoelectric conversion unit is arranged, between the firstsemiconductor substrate and the first insulating film; wherein aninterface of a region where the second element isolation portion isprovided, between the second semiconductor substrate and the secondinsulating film, is arranged at a second depth with respect to aninterface of a region where the amplifying transistor is arranged,between the second semiconductor substrate and the second insulatingfilm; and wherein the first depth is shallower than the second depth. 2.The solid-state imaging device according to claim 1, wherein light isincident on the first semiconductor substrate from a second principalsurface side thereof, the second principal surface being opposite to thefirst principal surface of the first semiconductor substrate.
 3. Thesolid-state imaging device according to claim 2, further comprising: anelectrically-conductive pattern configured to electrically connect thefloating diffusion region and a gate electrode of the amplifyingtransistor, wherein the first principal surface of the firstsemiconductor substrate faces a principal surface of the secondsemiconductor substrate on which the gate electrode of the amplifyingtransistor is arranged, the electrically-conductive pattern beinginterposed therebetween.
 4. The solid-state imaging device according toclaim 1, wherein the second element isolation portion is one of LOCOSisolation and STI isolation.
 5. The solid-state imaging device accordingto claim 1, wherein the first element isolation portion is one of PNisolation, mesa-type insulator isolation, and EDI isolation.
 6. Thesolid-state imaging device according to claim 1, wherein at least two ofthe plurality of pixels share the floating diffusion region.
 7. Thesolid-state imaging device according to claim 1, wherein thephotoelectric conversion unit comprises: a second conductivity typefirst semiconductor region configured to be in contact with the firstinsulating film; a first conductivity type second semiconductor regionprovided on an opposite side of the first semiconductor region, to aside thereof on which the first insulating film is provided; and asecond conductivity type third semiconductor region provided on anopposite side of the second semiconductor region, to a side thereof onwhich the first semiconductor region is provided.
 8. The solid-stateimaging device according to claim 7, wherein the first semiconductorregion extends through at least two of the plurality of pixels, andwherein the first semiconductor region and the floating diffusion regionare provided with a predetermined distance therebetween.
 9. Thesolid-state imaging device according to claim 7, wherein the firstsemiconductor region extends through at least two of the plurality ofpixels, and wherein the first semiconductor region defines a channelwidth of the transferring transistor.
 10. The solid-state imaging deviceaccording to claim 7, wherein a second conductivity type fourthsemiconductor region is provided on a opposite side of the floatdiffusion region, to the first insulating film, and wherein when thefirst semiconductor region and the fourth semiconductor region areprojected in a direction of the first insulating film, a region ontowhich the first semiconductor region is projected doesn't overlap with aregion onto which the fourth semiconductor is projected.
 11. Thesolid-state imaging device according to claim 7, wherein a contact plugconfigured to supply a voltage to the first semiconductor region or thethird semiconductor region is provided in a region other than the firstpixel region, but not provided in the first pixel region.
 12. Thesolid-state imaging device according to claim 1, wherein the floatingdiffusion regions are provided at a pitch of 3 micrometers or less. 13.A solid-state imaging device comprising a plurality of pixels, eachincluding: a photoelectric conversion unit; a floating diffusion region;a transferring transistor including a transferring gate electrodeconfigured to transfer signal charge generated at the photoelectricconversion unit to the floating diffusion region; an amplifyingtransistor configured to output a signal based on an amount of electriccharge of the floating diffusion region; and a resetting transistorconfigured to reset a voltage of the floating diffusion region, thesolid-state imaging device further comprising; a first semiconductorsubstrate and a second semiconductor substrate, wherein a plurality ofphotoelectric conversion units and a plurality of floating diffusionregions are arranged in the first semiconductor substrate; wherein oneof PN isolation, mesa-type insulator isolation, or EDI isolation isprovided in the first semiconductor substrate, configured toelectrically isolate at least a part of the plurality of photoelectricconversion units and at least a part of the plurality of floatingdiffusion regions from each other; wherein a plurality of the amplifyingtransistors and a plurality of the resetting transistors are arranged inthe second semiconductor substrate; wherein one of LOCOS isolation orSTI isolation is provided in the second semiconductor substrate,configured to electrically isolate at least a part of the plurality ofthe amplifying transistors and at least a part of the plurality of theresetting transistors from each other; wherein light is incident on thefirst semiconductor substrate from a second principal surface sidethereof, the second principal surface being opposite to a firstprincipal surface of the first semiconductor substrate; and anelectrically-conductive pattern configured to electrically connect thefloating diffusion region and a gate electrode of the amplifyingtransistor, wherein the first principal surface of the firstsemiconductor substrate faces a principal surface of the secondsemiconductor substrate on which the gate electrode of the amplifyingtransistor is arranged, the electrically-conductive pattern beinginterposed therebetween.
 14. A solid-state imaging device comprising aplurality of pixels, each including: a photoelectric conversion unit; afloating diffusion region; a transferring transistor including atransferring gate electrode configured to transfer signal chargegenerated at the photoelectric conversion unit to the floating diffusionregion; an amplifying transistor configured to output a signal based onan amount of electric charge of the floating diffusion region; and aresetting transistor configured to reset a voltage of the floatingdiffusion region, the solid-state imaging device further comprising; asignal processing circuit for processing a signal output from theplurality of pixels; and a first semiconductor substrate and a secondsemiconductor substrate, wherein a first insulating film is provided ona first principal surface of the first semiconductor substrate, whereinthe first semiconductor substrate includes a first pixel region; whereina plurality of photoelectric conversion units and a plurality offloating diffusion regions are arranged in the first pixel region;wherein a first element isolation portion is provided in the first pixelregion, configured to electrically isolate at least a part of theplurality of photoelectric conversion units and at least a part of theplurality of floating diffusion regions from each other; wherein asecond insulating film is provided on the second semiconductorsubstrate; wherein the second semiconductor substrate includes a secondpixel region and a peripheral circuit region; wherein a plurality of theamplifying transistors and a plurality of the resetting transistors arearranged in the second pixel region; wherein a plurality of transistorsincluded in the signal processing circuit are arranged in the peripheralcircuit region; wherein a second element isolation portion is arrangedin the peripheral circuit region, configured to electrically isolate atleast a part of the plurality of transistors from each other; wherein aninterface of a region where the first element isolation portion isprovided, between the first semiconductor substrate and the firstinsulating film, is arranged at a first depth with respect to aninterface of a region where the photoelectric conversion unit isarranged, between the first semiconductor substrate and the firstinsulating film; wherein an interface of a region where the secondelement isolation portion is provided, between the second semiconductorsubstrate and the second insulating film, is arranged at a second depthwith respect to an interface of a region where the transistor includedin the signal processing circuit is arranged, between the secondsemiconductor substrate and the second insulating film; and wherein thefirst depth is shallower than the second depth.
 15. The solid-stateimaging device according to claim 14, wherein light is incident on thefirst semiconductor substrate from a second principal surface sidethereof, the second principal surface being opposite to the firstprincipal surface of the first semiconductor substrate.
 16. Thesolid-state imaging device according to claim 15, further comprising: anelectrically-conductive pattern configured to electrically connect thefloating diffusion region and a gate electrode of the amplifyingtransistor, wherein the first principal surface of the firstsemiconductor substrate faces a principal surface of the secondsemiconductor substrate on which the gate electrode of the amplifyingtransistor is arranged, the electrically-conductive pattern beinginterposed therebetween.
 17. The solid-state imaging device according toclaim 14, wherein the first element isolation portion is one of PNisolation, mesa-type insulator isolation, and EDI isolation, and whereinthe second element isolation portion is one of LOCOS isolation and STIisolation.
 18. A solid-state imaging device comprising a plurality ofpixels, each including: a photoelectric conversion unit; a floatingdiffusion region; a transferring transistor including a transferringgate electrode configured to transfer signal charge generated at thephotoelectric conversion unit to the floating diffusion region; anamplifying transistor configured to output a signal based on an amountof electric charge of the floating diffusion region; and a resettingtransistor configured to reset a voltage of the floating diffusionregion, the solid-state imaging device further comprising; a firstsemiconductor substrate, wherein a first insulating film is provided ona first principal surface of the first semiconductor substrate, whereinthe first semiconductor substrate includes a first pixel region; whereina plurality of the photoelectric conversion units and a plurality of thefloating diffusion regions are arranged in the first pixel region;wherein a first element isolation portion is arranged in the first pixelregion, configured to electrically isolate at least a part of theplurality of photoelectric conversion units and at least a part of theplurality of floating diffusion regions from each other; wherein aplurality of amplifying transistors and a plurality of resetting regionsare arranged in a second pixel region other than the first pixel region;wherein an interface between the first semiconductor substrate and thefirst insulating film is substantially flat through the first pixelregion; and wherein light is incident on the first semiconductorsubstrate from a second principal surface side thereof, the secondprincipal surface being opposite to the first principal surface of thefirst semiconductor substrate; and a second semiconductor substrate; andan electrically-conductive pattern configured to electrically connectthe floating diffusion region and a gate electrode of the amplifyingtransistor, wherein the second semiconductor substrate includes thesecond pixel region, and wherein the first principal surface of thefirst semiconductor substrate faces a principal surface of the secondsemiconductor substrate, on which the gate electrode of the amplifyingtransistor is arranged, the electrically-conductive pattern beinginterposed therebetween.